A wide variety of roadside barriers have been developed in recent years out of concern for the motorist and for the structures normally provided along a vehicle path such as an expressway, highway, road or street.
The road hazard may be any of a variety of structures of sufficient mass or rapidity to endanger the motorist traveling at high speed should, because of misadventure, operator failure or impact with another vehicle, a vehicle be directed or misdirected toward the hazard. The latter may be post for the traffic or roadway lighting or signs, a pylon, post or other pedestal supporting an overpass or utility lines, or simply an abutment which may be required in the design of the road.
Generally it has been the practice, especially in recent years, to provide upstream of the hazard in the direction of vehicle travel, a safety barrier of some sort to cushion any untoward travel toward the abutment.
For example, yieldable fences may be provided to direct a vehicle back into the traveling lane or along a shoulder flanking the hazard. Such systems have had the disadvantage that they may be torn away should they receive an impact at an improper angle or excessively high speed or from an especially heavy vehicle; they also may result in a deflection of the vehicle in an uncontrolled manner into the path of moving traffic creating danger not only to the occupants of the misdirected vehicle but also to occupants of other vehicles in the traffic lane.
Hence efforts to improve vehicular safety have concentrated upon devices designed to cushion the impact without deflecting the vehicle. Typical of such devices are flexible-wall structures containing yieldable materials such as water or sand, which take up a portion of the impact energy before they are dispersed or broken. Such devices have been found to be disadvantageous in many cases because they do not provide a sufficiently gradual deceleration of the vehicle to prevent damage thereto and injury to its occupants.
Considerably more satisfactory devices have been developed as described, for example, in my U.S. Pat. No. 3,881,697, which refers, in turn, to earlier systems found in U.S. Pat. Nos. 3,704,861 and 3,784,167, which may also be consulted in this connection.
Reference may be had also to U.S. Pat. No. 2,088,087, No. 2,134,624, No. 3,503,600, No. 3,606,248, No. 3,643,924, No. 3,674,115, No. 3,680,662, and No. 3,693,840 which were cited in the file of Ser. No. 407,998, the application upon which U.S. Pat. No. 3,881,697 issued.
For the details of the foamed synthetic-resin material, thin walled tubular structure, positioning of the posts and the like, my U.S. Pat. No. 3,881,697 may be consulted.
As noted, the system of U.S. Pat. No. 3,881,697 has the advantage that it provides a plurality of deflectible posts of increasing density and height in the direction of traveling toward the hazard or barrier and which gradually brings the vehicle to a standstill without impact against the hazard primarily by frictional engagement with the vehicle body and with minimal damage to the vehicle.
This is important because it also protects the occupants of the vehicle during the deceleration thereof.
In the system of U.S. Pat. No. 3,881,697, this is achieved by providing an array of upright but deflectible posts which extend longitudinally in the direction of travel toward the hazard and in the area ahead of the obstacle. The elongated bodies or posts are disturbed upon impact and are bent over in the direction of travel, thereby absorbing kinetic energy by deformation and by frictionally rubbing against the vehicle body.
It is important in that system that the absorption of kinetic energy be carried out over a fairly extended distance, corresponding to the length of the array, with damage to the vehicle being prevented because the vehicle tends to override the bands of the posts.
In the design of all such barriers, however, there is usually a compromise between the need to bring the vehicle to a complete stop before it reaches the hazard and the desire to carry out the deceleration as gradually as possible so that neither the vehicle nor its occupants will suffer injury because of an excessively rapid deceleration.
Test have shown that the barrier described in U.S. Pat. No. 3,881,697 can bring most vehicles traveling at speeds up to 100 km/hr, to a complete stop without noticeable damage to the vehicle, injury to the occupants, or impact with the road hazard.
However, although the latter system affords a significant advance from a safety point of view it has the disadvantage that many of the upright bodies are permanently deformed (i.e. bent) by the impact and as a result of the energy absorption. In the earlier system straightening of these bodies was time-consuming and frequently unsuccessful, while replacement of the device was expensive and authorities responsible for their installation have had to reckon with considerable expenditures in this connection.
The high cost is a result, in part, of the fact that the uptight bodies generally comprise an outer tube drawn or rolled from steel sheet and a synthetic foam filling and/or lining which is not expensive.